1. Field of the Invention
This invention relates to a covered lead wire for vehicles, and, particularly, to a covered lead wire for vehicles having good lead wire protective properties such as abrasion resistance and scrape resistance, and also capable of making the cover of a lead wire thinner.
2. Description of Prior Art
Covered lead wires for vehicles are slender covered lead wires used in vehicles such as automobiles, two-wheeled or three-wheeled motor vehicles and electric railcars, and they are used, for example, in a wire harness used for transmitting various kinds of information to an instrument panel of vehicles or transmitting various kinds of signals from an operation panel to other portions. The wire harness is required particularly for its cover to be endowed with abrasion resistance, scrape resistance (or scratch resistance), thermal deformation resistance, thermal aging resistance, cold resistance, mechanical properties such as elongation, etc. and electrical properties such as volume resistivity and dielectric breakdown voltage.
Conventionally used for covering lead wires for vehicles are non-rigid polyvinyl chloride resin compositions comprising polyvinyl chloride as its main ingredient, which are produced by extrusion to give a cover of usually 1 to 3 mm in thickness in order to satisfy the above properties required.
Incidentally, there is recently a demand for the cover to have a thickness of as thin as about 0.1 to 0.5 mm for the purpose of weight-saving and improving the wiring workability. In the conventional polyvinyl chloride compositions used for the covered lead wire for vehicles, however, the cover thickness reduced to about 0.1 to 0.5 mm may cause a problem of a considerable lowering of the protective properties such as abrasion resistance and scrape resistance.
To solve such a problem, it may be contemplated to use nylon, PBT, polyester resins, fluorine resins or the like as a substitute resin that can retain such protective properties even with reduced thickness of the cover. These resins, however, have drawbacks such that they have poor processability, have insufficient elongation, have poor wiring workability because of high hardness, or result in high cost. Moreover, they have disadvantages such that the process for producing covered lead wires for vehicles that has been fitted to the polyvinyl chloride resins conventionally used can not be used as they are, so that there can be a problem that a change of production process may result in an increase in the cost of products.